Depth profiling can be used for determining the spatial distribution of chemical elements in a sample, along the direction perpendicular to the sample's surface. Such information has great importance in various research and technological fields, particularly, for example, for inspection in VLSI wafer production lines.
Characterization methods that can determine compositional profiles across nanometer thick layered structures are of utmost importance to ultrathin gate oxide based devices, in particular, and to the current microelectronic science and industry in general. Such an example is the process dependent nitrogen distribution in silicon oxynitride (SiON) films, where nitrogen atoms are intentionally added to the SiO2 network to obtain improved diffusion barrier properties and enhanced immunity from hot carrier damage.
As depth profiling probes, secondary ion mass spectroscopy (SIMS) and Ar milling in core electron spectroscopy are commonly used. However, these destructive tools frequently induce major profile distortions. High depth profiling accuracy was demonstrated with nondestructive angle resolved x-ray photoelectron spectroscopy (ARXPS) of thin structures up to about 10 nm thick. ARXPS requires relatively long measurements and careful interpretation of a non-unique solution associated with an ill-defined inverse problem. Its analysis is largely improved by considering the role of elastic scattering events, and considerable progress can be achieved by evaluating also the background and satellite line intensities.
An alternative approach, which does not rely on the analysis of line intensities, has been proposed for nondestructive profiling: controlled surface charging (CSC). CSC extracts spatial information from the energy axis of the spectrum while creating potential gradients across the studied volume. Extension of CSC to consistent chemically resolved electrical measurements (CREM) has been demonstrated. CREM and CSC are both non-contact methods, proposing unique capabilities, down to atomic scale resolution of the electrostatic potential.